Holographic light detection and ranging

ABSTRACT

A light detection and ranging system arranged to scan a scene comprises a light source arranged to output light having a first characteristic. A spatial light modulator is arranged to receive the light from the light source and output spatially-modulated light in accordance with computer-generated holograms represented thereon. A holographic controller is arranged to output a plurality of holograms to the spatial light modulator. Each hologram is arranged to form a corresponding light footprint within the scene. The holographic controller is further arranged to change the position of the light footprint within the scene. A light detector is arranged to receive light having the first characteristic from the scene and output a light response signal. In embodiments, a first plurality of holograms are arranged to provide a first scan within the scene, and the holographic controller is arranged to receive the light response signal in response to the first scan and determine a second plurality of holograms based on a property of the light response signal.

FIELD

The present disclosure relates to a light projector. More specifically,the present disclosure relates to a holographic projector, holographicprojection system, a method of controlling a projector and a method ofcontrolling a holographic projection system. Embodiments relate to alight detection and ranging system. Some embodiments relate to a methodof light detection and ranging. Some embodiments relate to a method ofcontrolling the light footprint in a light detection and ranging system.Some embodiments relate to a method of scanning a scene with acomputer-controlled light footprint.

BACKGROUND AND INTRODUCTION

Light scattered from an object contains both amplitude and phaseinformation. This amplitude and phase information can be captured on,for example, a photosensitive plate by well-known interferencetechniques to form a holographic recording, or “hologram”, comprisinginterference fringes. The hologram may be reconstructed by illuminationwith suitable light to form a two-dimensional or three-dimensionalholographic reconstruction, or replay image, representative of theoriginal object.

Computer-generated holography may numerically simulate the interferenceprocess. A computer-generated hologram, “CGH”, may be calculated by atechnique based on a mathematical transformation such as a Fresnel orFourier transform. These types of holograms may be referred to asFresnel or Fourier holograms. A Fourier hologram may be considered aFourier domain representation of the object or a frequency domainrepresentation of the object. A CGH may also be calculated by coherentray tracing or a point cloud technique, for example.

A CGH may be encoded on a spatial light modulator, “SLM”, arranged tomodulate the amplitude and/or phase of incident light. Light modulationmay be achieved using electrically-addressable liquid crystals,optically-addressable liquid crystals or micro-mirrors, for example.

The SLM may comprise a plurality of individually-addressable pixelswhich may also be referred to as cells or elements. The light modulationscheme may be binary, multilevel or continuous.

Alternatively, the device may be continuous (i.e. is not comprised ofpixels) and light modulation may therefore be continuous across thedevice. The SLM may be reflective meaning that modulated light is outputfrom the SLM in reflection. The SLM may equally be transmissive meaningthat modulated light is output from the SLM is transmission.

A holographic projector for imaging may be provided using the describedtechnology. Such projectors have found application in head-up displays,“HUD”, and head-mounted displays, “HMD”, including near-eye devices, forexample.

SUMMARY

Aspects of an invention are defined in the appended independent claims.

There is provided a method of light detection and ranging comprisingilluminating a scene with spatially modulated light by outputting aplurality of computer-generated holograms to a spatial light modulatorand illuminating the spatial light modulator with light having a firstcharacteristic. Each hologram is arranged to form a corresponding lightfootprint within the scene. The method may further comprise moving thelight footprint within the scene. The method may also comprise receivingreflected spatially modulated light from the scene.

In accordance with the present disclosure, the light footprint may makediscrete movements from one part of the scene to another part of thescene. In particular, the light footprint may be instantaneouslyrepositioned within the scene. It may be said that the light footprintjumps from a first point in the scene to a second point in the scene.This achieved by using dynamic holography to form the light footprint.The method may be used to dynamically change the size, shape,orientation and/or position of the light footprint.

The method may further comprise moving the spatially modulated lightback and forth between two or more areas of the scene in order toperform an interleaved scan of two or more areas of the scene.

The method may further comprise intelligent scanning of the scene inwhich feedback from a light detector is used to determine how and whereto perform the next scan. This may comprise selecting at least onecomputer-generated hologram from a memory or calculating at least onecomputer-generated hologram including calculating at least onecomputer-generated hologram in real-time based on a received signal.

The term “light footprint” is used herein to refer to the illuminationpattern formed in the scene by each hologram. The light footprint istherefore an area of light within the scene. The light may be pulsed.The light may have uniform brightness across its area. The lightfootprint may be characterised by its size, shape and orientation. Thelight detection and ranging system disclosed herein may be used to forma temporal sequence of varying and/or moving light footprints within ascene. Advantageously, the dynamically-reconfigurable holographictechnique disclosed herein may be used to control parameters of thelight footprint and the position of the light footprint in real-time.

The term “hologram” is used to refer to the recording which containsamplitude and/or phase information about the object. The term“holographic reconstruction” is used to refer to the opticalreconstruction of the object which is formed by illuminating thehologram. The term “replay field” is used to refer to the plane in spacewhere the holographic reconstruction is formed.

The terms “encoding”, “writing” or “addressing” are used to describe theprocess of providing the plurality of pixels of the SLM with a respectplurality of control values which respectively determine the modulationlevel of each pixel. It may be said that the pixels of the SLM areconfigured to “display” a light modulation distribution in response toreceiving the plurality of control values.

The term “light” is used herein in its broadest sense. Embodiments areequally applicable to visible light, infrared light and ultravioletlight, and any combination thereof.

Embodiments describe monochromatic light footprints by way of exampleonly. In embodiments, the light footprint is a polychromatic lightfootprint. In embodiments, a composite colour light footprint isprovided by combining a plurality of single colour light footprints. Inembodiments, a plurality of single colour computer-generated hologramsmay be used to form each composite colour light footprint. Suchwavelength diversity can increase throughput.

Embodiments describe 1D and 2D light footprints by way of example only.In other embodiments, the light footprint is a 3D light footprint. Thatis, in embodiments, each computer-generated hologram forms a 3Dholographic reconstruction.

BRIEF DESCRIPTION OF THE DRAWINGS

Specific embodiments are described by way of example only with referenceto the following figures:

FIG. 1 is a schematic showing a reflective SLM producing a holographicreconstruction on a screen;

FIG. 2A illustrates a first iteration of an example Gerchberg-Saxtontype algorithm;

FIG. 2B illustrates the second and subsequent iterations of the exampleGerchberg-Saxton type algorithm;

FIG. 3 is a schematic of a reflective LCOS SLM;

FIG. 4 shows a LIDAR system in accordance with embodiments;

FIG. 5 also shows a LIDAR system in accordance with a first group ofembodiments;

FIG. 6 shows a scanning LIDAR system in accordance with the first groupof embodiments;

FIGS. 7A, 7B, 7C and 7D show example first light footprints and secondlight footprints in accordance with the first group of embodiments;

FIG. 8 shows a LIDAR system using interleaved holograms in accordancewith a second group of embodiments;

FIG. 9 shows an alternative configuration for interleaving holograms inaccordance with the second group of embodiments;

FIG. 10 shows interleaved holograms for scanning different areas of thescene in different directions in accordance with the second group ofembodiments;

FIG. 11 shows interleaved holograms forming a first light footprint of afirst size and a second light footprint of a second size smaller thanthe first size in accordance with the second group of embodiments;

FIG. 12 shows a feedback system for determining a plurality ofcomputer-generated holograms based on a received signal from the lightdetector in accordance with a third group of embodiments;

FIGS. 13A, 13B, 13C and 13D show example first and second scans inaccordance with the third group of embodiments;

FIG. 14 shows an example of an angular magnification system; and

FIG. 15 illustrates a method for detecting and ranging of an object inaccordance with embodiments.

The same reference numbers will be used throughout the drawings to referto the same or like parts.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention is not restricted to the embodiments described inthe following but extends to the full scope of the appended claims. Thatis, the present invention may be embodied in different forms and shouldnot be construed as limited to the described embodiments.

Terms of a singular form may include plural forms unless specifiedotherwise.

A structure described as being formed at an upper portion/lower portionof another structure or on/under the other structure should be construedas including a case where the structures contact each other and,moreover, a case where a third structure is disposed there between.

In describing a time relationship—for example, when the temporal orderof events is described as “after”, “subsequent”, “next”, “before” orsuchlike—the present disclosure should be taken to include continuousand non-continuous events unless otherwise specified. For example, thedescription should be taken to include a case which is not continuousunless wording such as “just”, “immediate” or “direct” is used.

Although the terms “first”, “second”, etc. may be used herein todescribe various elements, these elements are not limited by theseterms. These terms are only used to distinguish one element fromanother. For example, a first element could be termed a second element,and, similarly, a second element could be termed a first element,without departing from the scope of the appended claims.

Features of different embodiments may be partially or overall coupled toor combined with each other, and may be variously inter-operated witheach other. Embodiments may be carried out independently from eachother, or may be carried out together in co-dependent relationship.

It has been found that a holographic reconstruction of acceptablequality can be formed from a “hologram” containing only phaseinformation related to the original object. Such a holographic recordingmay be referred to as a phase-only hologram. Embodiments relate tophase-only holography by way of example only. That is, in embodiments,the spatial light modulator applies only a phase-delay distribution toincident light. In embodiments, the phase delay applied by each pixel ismulti-level. That is, each pixel may be set at one of a discrete numberof phase levels.

In embodiments, the computer-generated hologram is a Fourier transformof the object for reconstruction. In these embodiments, it may be saidthat the hologram is a Fourier domain or frequency domain representationof the object. FIG. 1 shows an embodiment using a reflective SLM todisplay a phase-only Fourier hologram and produce a holographicreconstruction at a replay field.

A light source 110, for example a laser or laser diode, is disposed toilluminate the SLM 140 via a collimating lens 111. The collimating lenscauses a generally planar wavefront of light to be incident on the SLM.The direction of the wavefront is off-normal (e.g. two or three degreesaway from being truly orthogonal to the plane of the transparent layer).The arrangement is such that light from the light source is reflectedoff a mirrored rear surface of the SLM and interacts with aphase-modulating layer to form an exit wavefront 112. The exit wavefront112 is applied to optics including a Fourier transform lens 120, havingits focus at a screen 125.

The Fourier transform lens 120 receives a beam of phase-modulated lightfrom the SLM and performs a frequency-space transformation to produce aholographic reconstruction at the screen 125.

Light is incident across the phase-modulating layer (i.e. the array ofphase modulating elements) of the SLM. Modulated light exiting thephase-modulating layer is distributed across the replay field. Notably,in this type of holography, each pixel of the hologram contributes tothe whole reconstruction. That is, there is not a one-to-one correlationbetween specific points on the replay image and specificphase-modulating elements.

In these embodiments, the position of the holographic reconstruction inspace is determined by the optical power of the Fourier transform lens.In the embodiment shown in FIG. 1 , the Fourier transform lens is aphysical lens. That is, the Fourier transform lens is an optical Fouriertransform lens and the Fourier transform is performed optically.However, in other embodiments, the Fourier transform is performedcomputationally by including lensing data in the holographic data. Thatis, the hologram includes data representative of a lens as well as datarepresenting the object. It is known in the field of computer-generatedhologram how to calculate holographic data representative of a lens. Forexample, a phase-only holographic lens may be formed by calculating thephase delay caused by each point of the lens owing to its refractiveindex and spatially-variant optical path length. For example, theoptical path length at the centre of a convex lens is greater than theoptical path length at the edges of the lens. An amplitude-onlyholographic lens may be formed by a Fresnel zone plate. It is also knownin the art of computer-generated hologram how to combine holographicdata representative of a lens with holographic data representative ofthe object so that a Fourier transform can be performed without the needfor a physical Fourier lens. In embodiments, lensing data is combinedwith the holographic data by simple vector addition. Alternatively, inother embodiments, the Fourier transform lens is omitted such that theholographic reconstruction takes place in the far-field. In furtherembodiments, the hologram may include grating data—that is, dataarranged to perform the function of a grating such as beam steering.Again, it is known in the field of computer-generated hologram how tocalculate such holographic data and combine it with holographic datarepresentative of the object. For example, a phase-only holographicgrating may be formed by modelling the phase delay caused by each pointon the surface of a blazed grating. An amplitude-only holographicgrating may be simply superimposed on an amplitude-only hologramrepresentative of an object to provide beam steering of anamplitude-only hologram.

A Fourier hologram of a 2D image may be calculated in a number of ways,including using algorithms such as the Gerchberg-Saxton algorithm. TheGerchberg-Saxton algorithm may be used to derive phase information inthe Fourier domain from amplitude information in the spatial domain(such as a 2D image). That is, phase information related to the objectmay be “retrieved” from intensity, or amplitude, only information in thespatial domain. Accordingly, a phase-only Fourier transform of theobject may be calculated.

In embodiments, a computer-generated hologram is calculated fromamplitude information using the Gerchberg-Saxton algorithm or avariation thereof. The Gerchberg Saxton algorithm considers the phaseretrieval problem when intensity cross-sections of a light beam,I_(A)(x,y) and I_(B)(x,y), in the planes A and B respectively, are knownand I_(A)(x,y) and I_(B)(x,y) are related by a single Fourier transform.With the given intensity cross-sections, an approximation to the phasedistribution in the planes A and B, Φ_(A)(x,y) and Φ_(B)(x,y)respectively, is found. The Gerchberg-Saxton algorithm finds solutionsto this problem by following an iterative process.

The Gerchberg-Saxton algorithm iteratively applies spatial and spectralconstraints while repeatedly transferring a data set (amplitude andphase), representative of I_(A)(x,y) and I_(B)(x,y), between the spatialdomain and the Fourier (spectral) domain. The spatial and spectralconstraints are I_(A)(x,y) and I_(B)(x,y) respectively. The constraintsin either the spatial or spectral domain are imposed upon the amplitudeof the data set. The corresponding phase information is retrievedthrough a series of iterations.

In embodiments, the hologram is calculated using an algorithm based onthe Gerchberg-Saxton algorithm such as described in British patent2,498,170 or 2,501,112 which are hereby incorporated in their entiretyby reference.

In accordance with embodiments, an algorithm based on theGerchberg-Saxton algorithm retrieves the phase information ψ[u,v] of theFourier transform of the data set which gives rise to a known amplitudeinformation T[x,y]. Amplitude information T[x,y] is representative of atarget image (e.g. a photograph). The phase information ψ[u,v] is usedto produce a holographic representative of the target image at an imageplane.

Since the magnitude and phase are intrinsically combined in the Fouriertransform, the transformed magnitude (as well as phase) contains usefulinformation about the accuracy of the calculated data set. Thus, thealgorithm may provide feedback on both the amplitude and the phaseinformation.

An example algorithm based on the Gerchberg-Saxton algorithm inaccordance with embodiments of the present disclosure is described inthe following with reference to FIG. 2 . The algorithm is iterative andconvergent. The algorithm is arranged to produce a hologram representingan input image. The algorithm may be used to determine an amplitude-onlyhologram, a phase-only hologram or a fully complex hologram. Exampledisclosed herein relate to producing a phase-only hologram by way ofexample only. FIG. 2A illustrates the first iteration of the algorithmand represents the core of the algorithm. FIG. 2B illustrates subsequentiterations of the algorithm.

For the purpose of this description, the amplitude and phase informationare considered separately although they are intrinsically combined toform a composite complex data set. With reference to FIG. 2A, the coreof the algorithm can be considered as having an input comprising firstcomplex data and an output comprising a fourth complex data. Firstcomplex data comprises a first amplitude component 201 and a first phasecomponent 203. Fourth complex data comprises a fourth amplitudecomponent 211 and a fourth phase component 213. In this example, theinput image is two-dimensional. The amplitude and phase information aretherefore functions of the spatial coordinates (x,y) in the farfieldimage and functions of (u,v) for the hologram field. That is, theamplitude and phase at each plane are amplitude and phase distributionsat each plane.

In this first iteration, the first amplitude component 201 is the inputimage 210 of which the hologram is being calculated. In this firstiteration, the first phase component 203 is a random phase component 230merely used as a starting point for the algorithm. Processing block 250performs a Fourier transform of the first complex data to form secondcomplex data having a second amplitude component (not shown) and asecond phase information 205. In this example, the second amplitudecomponent is discarded and replaced by a third amplitude component 207by processing block 252. In other examples, processing block 252performs different functions to produce the third amplitude component207. In this example, the third amplitude component 207 is adistribution representative of the light source. Second phase component205 is quantised by processing block 254 to produce third phasecomponent 209. The third amplitude component 207 and third phasecomponent 209 form third complex data. The third complex data is inputto processing block 256 which performs an inverse Fourier transform.Processing block 256 outputs fourth complex data having the fourthamplitude component 211 and the fourth phase component 213. The fourthcomplex data is used to form the input for the next iteration. That is,the fourth complex data of the nth iteration is used to form the firstcomplex of the (n+1)th iteration.

FIG. 2B shows second and subsequent iterations of the algorithm.Processing block 250 receives first complex data having a firstamplitude component 201 derived from the fourth amplitude component 211of the previous iteration and a first phase component 213 correspondingto the fourth phase component of the previous iteration.

In this example, the first amplitude component 201 is derived from thefourth amplitude component 211 of the previous iteration as described inthe following. Processing block 258 subtracts the input image 210 fromthe fourth amplitude component 211 of the previous iteration to formfifth amplitude component 215. Processing block 260 scales the fifthamplitude component 215 by a gain factor α and subtracts it from theinput image 210. This is expressed mathematically by the followingequations:R _(n+1)[x,y]=F′{exp(iψ _(n)[u,v])}ψ_(n)[u,v]=∠F{n·exp(i∠R _(n)[x,y])}n=T[x,y]−α(|R _(n)[x,y]|−T[x,y])

Where:

F′ is the inverse Fourier transform;

F if the forward Fourier transform;

R is the replay field;

T is the target image;

∠ is the angular information;

ψ is the quantized version of the angular information;

ε is the new target magnitude, ε≥0; and

α is a gain element˜1.

The gain element α may be fixed or variable. In examples, the gainelement α is determined based on the size and rate of the incomingtarget image data.

Processing blocks 250, 252, 254 and 256 function as described withreference to FIG. 2A. In the final iteration, a phase-only hologram ψ(u,v) representative of the input image 210 is output. It may be said thatthe phase-only hologram ψ(u, v) comprises a phase distribution in thefrequency or Fourier domain.

In other examples, the second amplitude component is not discarded.Instead, the input image 210 is subtracted from the second amplitudecomponent and a multiple of that amplitude component is subtracted fromthe input image 210 to produce the third amplitude component 307. Inother examples, the fourth phase component is not fed back in full andonly a portion proportion to its change over, for example, the last twoiterations is fed back.

In embodiments, there is provided a real-time engine arranged to receiveimage data and calculate holograms in real-time using the algorithm. Inembodiments, the image data is a video comprising a sequence of imageframes. In other embodiments, the holograms are pre-calculated, storedin computer memory and recalled as needed for display on a SLM. That is,in embodiments, there is provided a repository of predeterminedholograms.

However, embodiments relate to Fourier holography and Gerchberg-Saxtontype algorithms by way of the example only. The present disclosure isequally applicable to Fresnel holography and holograms calculated byother techniques such as those based on point cloud methods.

The present disclosure may be implemented using any one of a number ofdifferent types of SLM. The SLM may output spatially modulated light inreflection or transmission. In embodiments, the SLM is a liquid crystalon silicon, “LCOS”, SLM but the present disclosure is not restricted tothis type of SLM.

A LCOS device is capable of displaying large arrays of phase onlyelements in a small aperture. Small elements (typically approximately 10microns or smaller) result in a practical diffraction angle (a fewdegrees) so that the optical system does not require a very long opticalpath. It is easier to adequately illuminate the small aperture (a fewsquare centimetres) of a LCOS SLM than it would be for the aperture of alarger liquid crystal device. LCOS SLMs also have a large apertureratio, there being very little dead space between the pixels (as thecircuitry to drive them is buried under the mirrors). This is animportant issue to lowering the optical noise in the replay field. Usinga silicon backplane has the advantage that the pixels are opticallyflat, which is important for a phase modulating device.

A suitable LCOS SLM is described below, by way of example only, withreference to FIG. 3 . An LCOS device is formed using a single crystalsilicon substrate 302. It has a 2D array of square planar aluminiumelectrodes 301, spaced apart by a gap 301 a, arranged on the uppersurface of the substrate. Each of the electrodes 301 can be addressedvia circuitry 302 a buried in the substrate 302. Each of the electrodesforms a respective planar mirror. An alignment layer 303 is disposed onthe array of electrodes, and a liquid crystal layer 304 is disposed onthe alignment layer 303. A second alignment layer 305 is disposed on theliquid crystal layer 304 and a planar transparent layer 306, e.g. ofglass, is disposed on the second alignment layer 305. A singletransparent electrode 307 e.g. of ITO is disposed between thetransparent layer 306 and the second alignment layer 305.

Each of the square electrodes 301 defines, together with the overlyingregion of the transparent electrode 307 and the intervening liquidcrystal material, a controllable phase-modulating element 308, oftenreferred to as a pixel. The effective pixel area, or fill factor, is thepercentage of the total pixel which is optically active, taking intoaccount the space between pixels 301 a. By control of the voltageapplied to each electrode 301 with respect to the transparent electrode307, the properties of the liquid crystal material of the respectivephase modulating element may be varied, thereby to provide a variabledelay to light incident thereon. The effect is to provide phase-onlymodulation to the wavefront, i.e. no amplitude effect occurs.

The described LCOS SLM outputs spatially modulated light in reflectionbut the present disclosure is equally applicable to a transmissive LCOSSLM. Reflective LCOS SLMs have the advantage that the signal lines, gatelines and transistors are below the mirrored surface, which results inhigh fill factors (typically greater than 90%) and high resolutions.Another advantage of using a reflective LCOS spatial light modulator isthat the liquid crystal layer can be half the thickness than would benecessary if a transmissive device were used. This greatly improves theswitching speed of the liquid crystal (a key point for projection ofmoving video images).

The inventor has previously disclosed various methods for providingimproved image projection using the holographic technique of the presentdisclosure. The inventor recognised that this holographic technique mayalso be used to form the basis of an improved LIDAR system.Specifically, the inventor recognised that the technique may be used towrite a sequence of computer-generated holograms to a spatial lightmodulator which scan a light footprint across a scene as required forLIDAR. Advantageously, the position of the light footprint within thescene may be changed by changing the computer-generated hologram. It maybe understood how a light detector may be synchronised with the lightsource and spatial light modulator in order to provide light detectionand ranging. The light has a first characteristic which means it may bedistinguished from other light received by the detector. The light maybe pulsed and temporally synchronised with the sequence of holograms. Inembodiments, the first characteristic is amplitude modulation at a firstfrequency. However, the light may be characterised in any other ways. Inembodiments, the first frequency is a radio frequency.

First Group of Embodiments

FIG. 4 shows an embodiment comprising a spatial light modulator 410arranged to direct light to a scene 400 and a light detector 420arranged to collected reflected light from the scene. Spatial lightmodulator 410 is arranged to receive light from a light source (notshown) and output spatially modulated light in accordance with adynamically-variable computer-generated hologram represented on thespatial light modulator 410. FIG. 4 shows the spatial light modulator410 outputting first spatially modulated light 431 forming a first lightfootprint 451 in the scene 400 in accordance with a firstcomputer-generated hologram (not shown) represented on the spatial lightmodulator 410. FIG. 4 also shows the spatial light modulator 410outputting second spatially modulated light 432 forming a second lightfootprint 461 in the scene 400 in accordance with a secondcomputer-generated hologram (not shown) represented on the spatial lightmodulator 410.

The first computer-generated hologram and second computer-generatedhologram are displayed on the spatial light modulator at different timesin order to provide scanning. The spatial light modulator receives asequence of computer-generated holograms from a holographic controller(not shown) in order to form a corresponding temporal sequence of lightfootprints within the scene.

In some embodiments, the brightness of the light footprint issubstantially uniform across its area. In other embodiments, thebrightness of the light footprint is changed depending upon distancefrom the spatial light modulator (i.e. range). For example, thebrightness of light footprint may increase with distance from thespatial light modulator. In an embodiment, a first light footprinthaving a first brightness is formed at a first distance from the spatiallight modulator and a second footprint having a second brightness isformed at a second distance from the spatial light modulator, whereinthe first distance is greater than the second distance and the firstbrightness is greater than the second brightness. The first lightfootprint and second light footprint may be formed at substantially thesame time or they may be formed at different times. In an embodiment,the first light footprint and second light footprint are successivelight footprints of a temporal sequence of light footprints within thescene.

There is therefore provided a light detection and ranging, “LIDAR”,system arranged to scan a scene, the system comprising: a light sourcearranged to output light having a first characteristic; a spatial lightmodulator arranged to receive the light from the light source and outputspatially-modulated light in accordance with computer-generatedholograms represented on the spatial light modulator; a holographiccontroller arranged to output a plurality of computer-generatedholograms to the spatial light modulator, wherein eachcomputer-generated hologram is arranged to form a corresponding lightfootprint within the scene and the holographic controller is furtherarranged to change the position of the light footprint within the scene;and a light detector arranged to receive light having the firstcharacteristic from the scene and output a light response signal.

The holographic controller is arranged to move the light footprint bychanging the holographic pattern displayed on the spatial lightmodulator. In embodiments, the plurality of computer-generated hologramscomprise a first computer-generated hologram arranged to form a firstlight footprint at a first position in the scene and a secondcomputer-generated hologram arranged to form a second light footprint ata second position in the scene, wherein output of the secondcomputer-generated hologram immediately follows output of the firstcomputer-generated hologram.

LIDAR systems have been disclosed using moving optics, such as rotatingprims, to provide light scanning. However, such systems aresignificantly disadvantaged by their reliance on moving parts. Theholographic LIDAR system disclosed herein does not require moving opticsin order to provide light scanning. Instead, movement of the lightfootprint is provided by computational manipulation of the hologram.Again, it is known how in the field of computer-generated hologram howto calculate holographic data representative of a grating in order toprovide beam steering and combine it with holographic datarepresentative of an object (e.g. a light footprint). Properties of theholographic grating, such as periodicity, may be dynamically changed inorder to steer light to desired positions in the scene.

LIDAR systems using rotating prisms provide continuous scanning in onedirection by continuously rotating the prism at a predetermined speed.In contrast, the holographic LIDAR system disclosed herein allows thelight footprint to be dynamically repositioned within the scene withoutrestriction. In particular, the light footprint may be moved from oneposition in the scene to any other position in the scene withoutilluminating any intermediate positions. In this respect, it may be saidthat the light footprint may be instantaneously jumped from one positionin the scene to any other position in the scene. In embodiments, thefirst position is spatially separated from the second position. Thisprovides more flexible scanning in contrast to rotating prism systemswhich require the prism to rotate into position. Accordingly, theholographic LIDAR system of the present disclosure therefore providesmore flexible scanning and faster dynamic scanning. It may beunderstood, however, that the system is equally suitable for cases inwhich the first position is substantially adjacent the second position.FIG. 5 shows an embodiment in which the first light footprint 551 andsecond light footprint 561 are substantially adjacent.

FIG. 6 shows an embodiment in which the light footprint 651 is movedwithin the scene to illuminate a continuous area of the scene. That is,in embodiments, the light footprint is continuously repositioned so asto scan the light footprint within the scene. FIG. 6 shows a continuousscan but the present system is equally suitable to providing adiscontinuous scan.

The inventor further recognised that the computation nature of theholographic system can be exploited to instantaneously change propertiesof the light footprint for improved scanning. In embodiments, the firstlight footprint has a first area and the second light footprint has asecond area, wherein the first area is not equal to the second area.

FIG. 7A shows a first light footprint 751 and a second light footprint761 within a scene 700. The second light footprint 761 has an area lessthan that of the first light footprint 751. The system may be arrangedto scan a first area 750 of the scene 700 with the first light footprint751 and scan a second area 760 of the scene 700 with the second lightfootprint 761. The second light footprint 761 may be formed immediatelyafter the first light footprint 751, or vice versa. The smaller thelight footprint, the higher the spatial resolution of the system.Therefore, the holographic LIDAR system of the present disclosureenables the spatial resolution of the scanning to be dynamicallycontrolled. For example, in embodiments, it may be advantageous tochange the resolution of a scan.

If the light footprint size is decreased, it will become brighterbecause the method of projection is holographic (every pixel of thehologram contributes to every point in the reconstruction). Thisimproves the signal-to-noise ratio or increases the maximum range of thedevice. In an embodiment, a higher resolution scan is performed in atleast one area of a scene and a lower resolution scan is performed in atleast one other area of the scene. In an example, the system is arrangedto scan a road with a first light footprint and the curb with a secondlight footprint, wherein the first light footprint is larger than thesecond light footprint. Accordingly, the curb is scanned at a higherresolution than, for example, a vehicle ahead. This is because it may benecessary to know if there is a vehicle in front and its distance awaybut it may not be necessary to determine the width of the vehicle. Thehigher resolution scan of the curb provides accuracy of position.Therefore, in some embodiments, a relatively low resolution scan of thecentre of a scene is performed and at least one relatively highresolution scan of the periphery of the scene is performed. That is, theat least one scan of the periphery of the scene is of higher resolutionthan a scan of the centre of the scene.

In other embodiments, the holographic system is used to providefootprints of a different shape. FIG. 7B shows an embodiment in whichthe second light footprint 762 has a different shape to the first lightfootprint 752. That is, in embodiments, the first light footprint has afirst shape and the second light footprint has a second shape, whereinthe first shape is different to the second shape. It may be advantageousto use different shaped footprints for probing different areas of thescene or different objects within the scene. Therefore, a more flexibleLIDAR system is provided.

In embodiments, the holographic system is used to rotate the lightfootprint. FIG. 7C shows an embodiment in which the first lightfootprint 753 and second light footprint 763 have the same shape but indifferent orientations. That is, in embodiments, the first lightfootprint has a shape having a first orientation and the second lightfootprint has a shape having a second orientation, wherein the firstorientation is different to the second orientation. In examples,accurate positional information may be obtained by scanning in twodifferent directions. In other examples, the light response signal maybe increased or optimised by changing the orientation of the lightfootprint.

In embodiments, the shape is a substantially one-dimensional shape. Forexample, the light footprint may have a slit or line shape. FIG. 7Dshows an embodiment in which the first light footprint 754 isperpendicular to the second light footprint 764. A one-dimensionalfootprint provides a one-dimensional scan which is advantageous forquickly sweeping across a scene, for example, to see if any objects arepresent in the scene. It may be advantageous to perform aone-dimensional scan of a first area of the scene in a first directionand a one-dimensional scan of a second area of the scene in anorthogonal direction. That is, in embodiments, the first orientation isperpendicular to the second orientation.

Second Group of Embodiments—Interleaved Scanning

FIG. 8 shows an embodiment comprising a spatial light modulator 810arranged to direct light to a scene 800 and a light detector 820arranged to collect reflected light from the scene. Spatial lightmodulator 810 is arranged to receive light from a light source (notshown) and output spatially modulated light in accordance with adynamically-variable computer-generated hologram represented on thespatial light modulator 810. FIG. 8 shows the spatial light modulator810 outputting first spatially modulated light 831 forming a first lightfootprint 851 in the scene 800 in accordance with a firstcomputer-generated hologram (not shown) represented on the spatial lightmodulator 810. FIG. 8 also shows the spatial light modulator 810outputting second spatially modulated light 832 forming a second lightfootprint 861 in the scene 800 in accordance with a secondcomputer-generated hologram (not shown) represented on the spatial lightmodulator 810. The first computer-generated hologram and secondcomputer-generated hologram are displayed on the spatial light modulatorat different times in order to provide scanning. The spatial lightmodulator receives a sequence of computer-generated holograms 891, 895,892, 896, 893, 897, 894 from a holographic controller (not shown) inorder to form a corresponding temporal sequence of light footprintswithin the scene including first light footprint 851 and second lightfootprint 861.

FIG. 8 further shows a first plurality of computer-generated holograms891, 892, 893 arranged to form a plurality of first light footprints,including first light footprint 851, within a first area 850 of thescene 800. FIG. 8 also shows a second plurality of computer-generatedholograms 895, 896, 897 arranged to form a plurality of second lightfootprints, including second light footprint 861, within a second area860 of the scene 800.

The second light footprints, including second light footprint 861, andthe second plurality of computer-generated holograms 895, 896 and 897are hatched for illustrative purposes only to indicate that theycorrespond. However, it should be remembered that what is displayed onthe spatial light modulator is not simply optically translated onto thescene. Each computer-generated hologram is a diffractive pattern whichrecreates a corresponding light footprint at the scene by interference.There is not a one-to-one correlation between points in the hologram andpoints in the scene. Each point in the hologram contributes to everypoint in the corresponding light footprint. Likewise, the first lightfootprints, including first light footprint 851, and the first pluralityof computer-generated holograms 891, 892 and 893 are unhatched forillustrative purposes to indicate that they correspond.

The first plurality of computer-generated holograms 891, 892, 893 arearranged to provide a first scan 850 of the scene 800 in a firstdirection 880. Computer-generated hologram 893 corresponds to firstlight footprint 851. The second plurality of computer-generatedholograms 895, 896, 897 are arranged to provide a second scan 860 of thescene 800 in a second direction 885. Computer-generated hologram 897corresponds to second light footprint 861. Although only threecomputer-generated holograms are shown in FIG. 8 for each scan, thepresent disclosure encompasses using any number of computer-generatedholograms in each scan.

It may therefore be understood that, in embodiments, the plurality ofcomputer-generated holograms comprise a first plurality ofcomputer-generated holograms arranged to provide a first scan within thescene and a second plurality of computer-generated holograms arranged toprovide a second scan within the scene. FIG. 8 shows the first scan andthe second scan in different directions by way of example only. In otherembodiments, the first scan and second scan are scans in the samedirection.

FIG. 8 shows holograms of the first plurality of computer-generatedholograms and holograms of the second plurality of computer-generatedholograms being alternately output to spatial light modulator 810. Thatis, in embodiments, the first plurality of computer-generated hologramsand second plurality of computer-generated holograms are interleaved.However, the present disclosure encompasses any arrangement for theinterlacing. For example, FIG. 9 shows an alternative embodiment inwhich two holograms of the first plurality of computer-generatedholograms 991, 992, 993, 994 are interleaved with one hologram of thesecond plurality of computer-generated holograms 995, 996.

In embodiments, including the embodiments shown in FIGS. 8 and 9 , thefirst scan is a scan of a first area of the scene and the second scan isa scan of a second area of the scene, wherein the second area isspatially separated from the first area. It may be understood that theplurality of computer-generated holograms are arranged to scan the firstarea and second area by moving spatially-modulated light back and forthbetween the first area and second area. Again, as described above, LIDARsystems based on scanning optics cannot achieve this functionality whichallows for more rapid scanning of spatially separated areas of thescene.

FIG. 10 shows a scene 1000 comprises a first area 1050 and a second area1060. A first plurality of computer-generated holograms 1091, 1092, 1093are arranged to scan a first light footprint 1051 in a first direction1080 within a first area 1050. A second plurality of computer-generatedholograms 1095, 1096, 1097 are arranged to scan a second light footprint1061 in a second direction 1085 within a second area 1060. Accordingly,in embodiments, the first scan is a scan in a first direction of thefirst area of the scene and the second scan is a scan in a seconddirection of the second area of the scene. In embodiments, the secondscan may also be a scan of the first area. In embodiments, the secondscan is performed in the same direction as the first scan.

In accordance with embodiments, a first scan at a relatively lowresolution is interleaved with a second scan at a higher resolutionscan. Again, the smaller the light footprint, the higher the spatialresolution. FIG. 11 shows an embodiment in the which the secondfootprint 1161 has a smaller area than the first footprint 1051. It maytherefore be understood that, in embodiments, the first plurality ofcomputer-generated holograms are arranged to form a first lightfootprint having a first area and the second plurality ofcomputer-generated holograms are arranged to form a second lightfootprint having a second area, wherein the first area is not equal tothe second area.

In embodiments, the first light footprint has a substantiallyone-dimensional shape extending in a second direction and the secondlight footprint has a substantially one-dimensional shape extending in afirst direction.

The first and second interleaved scans may relate to the same ordifferent areas of the scene. Scanning the same area of the sceneconcurrently using different light footprints (e.g. a footprint of thefirst scan corresponding to a fine or high resolution scan and afootprint of the second scan corresponding to coarse or low resolutionscan) may provide different information about the area of the scene.Scanning different areas of the scene concurrently using the same ordifferent footprints can obtain information about the different areas ofthe scene. Since the first and second scans are interleaved, andtherefore performed concurrently, the information captured by both scansrelates to the scene at substantially the same point in time.

In accordance with embodiments, the first scan may comprise a stochasticscan, which projects a light footprint that is moved randomly around thescene (e.g. to different areas around a vehicle). When a feature withinthe scene is identified from the stochastic scan (e.g., from a lightresponse signal in response to the first scan) or otherwise, a secondscan of an area including the identified feature may be performed (e.g.at higher resolution). In embodiments, the stochastic scan iscontinuous, and one or more second (e.g. higher resolution) scans areinterleaved with the stochastic scan. In particular, high resolutionsecond scans may be performed concurrently with the stochastic scan, asdescribed above with reference to FIGS. 8 to 11 . Thus, the stochasticscan may be performed continuously, and second scans of limited durationmay be introduced, interleaved into the stochastic scan, as necessary.For example, a second, high resolution scan of a particular area may beadded, interleaved with the stochastic scan, when a feature is detectedwithin the area, and then removed when the high resolution scan iscomplete. Thus, new targets are continually identified by the continuousstochastic scan, and further detail of such identified targets aresubsequently obtained by the second scans. In alternative embodiments,the second scan may be performed instead of the stochastic scan (i.e.,the first and second scans are not concurrent). In this case, scanningalternates between the first and second scans.

Third Group of Embodiments—Intelligent Scanning

Embodiments provide a feedback system in which the results of a firstscan are used to determine the computer-generated holograms for a secondscan. The step of determining the computer-generated holograms for thesecond scan may comprise selecting the holograms from a repository ofholograms or calculating the holograms.

FIG. 12 shows an embodiment comprising a spatial light modulator 1210arranged to direct light to a scene 1200 and a light detector 1220arranged to collect reflected light from the scene. Spatial lightmodulator 1210 is arranged to receive light from a light source (notshown) and output spatially modulated light in accordance with adynamically-variable computer-generated hologram represented on thespatial light modulator 1210. FIG. 12 shows the spatial light modulator1210 outputting first spatially modulated light 1231 forming a firstlight footprint 1251 in the scene 1200 in accordance with a firstcomputer-generated hologram (not shown) represented on the spatial lightmodulator 1210.

FIG. 12 further shows light detector 1220 receiving reflected light 1241from the region of the scene 1200 illuminated by the first lightfootprint 1251. For example, the light may be reflected off an object inthe scene. In response to receiving the reflected light 1241, lightdetector 1220 outputs a light response signal 1274. A holographiccontroller 1270 is arranged to receive the light response signal 1274and determine a second plurality of computer-generated holograms.Holographic controller 1270 outputs holographic data 1272, comprisingthe second plurality of computer-generated holograms, to the spatiallight modulator 1210.

The holographic controller 1270 may assess a property of the lightresponse signal 1274 in order to determine the second plurality ofcomputer-generated holograms. In embodiments, the holographic controller1270 determines if the light response signal 1274 indicates that anobject is present in the area scanned with the first light footprint. Insome embodiments, the property of the light response signal 1274 is themaximum (or peak) intensity or average (or mean) intensity of the lightresponse signal 1274. In other embodiments, the property of the lightresponse signal 1274 is change in the intensity of the light responsesignal 1274 or a rate of change of intensity in the light responsesignal 1274. The property of the light response signal may be anyproperty of the light response signal 1274, or any feature in the lightresponse signal 1274, which may provide information about the areascanned or any objects in the area scanned. For example, the holographiccontroller 1270 may determine if the magnitude of the light responsesignal 1274 exceeds a threshold value. For example, in embodiments, theholographic controller 1270 determines that an object is present in afirst area scanned with the first light footprint 1251 and determines asecond plurality of computer-generated holograms arranged to scan thefirst area again at high resolution. For example, in other embodiments,the holographic controller 1270 determines that an object is not presentin a first area scanned with the first light footprint 1251 anddetermines a second plurality of computer-generated holograms arrangedto scan a second area of the scene with second light footprint 1261. Forexample, in other embodiments, the holographic controller 1270determines that the light response signal is inconclusive (for example,relatively noisy) and determines a second plurality ofcomputer-generated holograms arranged to scan the same area of the sceneagain but in a different direction.

In response to each computer-generated hologram of the second pluralityof computer-generated holograms, a corresponding second light footprint1261 is formed in the scene 1200. The second light footprint 1261 may bescanned within the scene 1200 as previously described. The spatial lightmodulator 1210 receives the second plurality of computer-generatedholograms from the holographic controller 1270 in order to form acorresponding temporal sequence of light footprints, including secondlight footprint 1261, within the scene 1200.

Therefore, in embodiments, the plurality of computer-generated hologramscomprise a first plurality of computer-generated holograms arranged toprovide a first scan within the scene, and the holographic controller isarranged to receive the light response signal in response to the firstscan and determine a second plurality of computer-generated hologramsbased on a property of the light response signal in response to thefirst scan. In embodiments, the second plurality of computer-generatedholograms are arranged to provide a second scan within the scene.

FIG. 13A shows an embodiment in which the first scan is a scan of afirst area 1350 of the scene 1300 with a first light footprint 1351 in afirst direction 1380. The second scan, corresponding to the secondplurality of computer-generated holograms, may be a scan of the firstarea 1350 or a second area 1360 of the scene 1300.

FIG. 13B shows an embodiment in which the first scan is a scan of afirst area of the scene and the second scan is a scan of a second areaof the scene, wherein the second area is spatially separated from thefirst area.

FIG. 13C shows an embodiment in which the first scan is a scan in afirst direction of the first area of the scene and the second scan is ascan in a second direction of the first area of the scene. Inembodiments, the second scan is performed using a second light footprinthaving a different size, shape and/or orientation to the first lightfootprint.

FIG. 13D shows an embodiment in which the first plurality ofcomputer-generated holograms are arranged to form a first lightfootprint having a first area and the second plurality ofcomputer-generated holograms are arranged to form a second lightfootprint having a second area, wherein the first area is not equal tothe second area.

In embodiments, the first area of the scene, which is scanned by thefirst scan, may be the same, part of, adjacent or spatially separatedfrom the second area of the scene, which is scanned by the second scan.

Variations for All Groups of Embodiments

In embodiments, the first light footprint has a substantiallyone-dimensional shape extending in a second direction and the secondlight footprint has a substantially one-dimensional shape extending in afirst direction.

In embodiments, the spatially light modulator is a phase-only spatiallight modulator. These embodiments are advantageous because no opticalenergy is lost by modulating amplitude. Accordingly, an efficientholographic projection system is provided. However, the presentdisclosure may be equally implemented on an amplitude-only spatial lightmodulator or an amplitude and phase modulator. It may be understood thatthe hologram will be correspondingly phase-only, amplitude-only orfully-complex.

Embodiments include an angular magnification system to increase thefield of view of the system. FIG. 14 shows an angular magnificationsystem 1425 arranged to receive spatially modulated light from a spatiallight modulator 1410 at a first angle. The angular magnification system1425 outputs spatially modulated light, at a second angle greater thanthe first angle, which illuminates the scene. FIG. 14 shows that theangular magnification system 1425 is arranged to receive light 1422 at afirst angle and output light 1424 at a second angle greater than thefirst angle. It may be said that the angular magnification systemmagnifies the angle of light of the spatially modulated light. That is,in embodiments, the LIDAR system further comprises an angularmagnification system arranged to magnify the angular deflection of thespatially-modulated light from the spatial light modulator.

In embodiments, the angular magnification is provided by refraction.That is, in embodiments, the angular magnification system is arranged torefract the spatially-modulated light. In embodiments, the angularmagnification system is arranged to receive the spatially modulatedlight at a first angle and output the spatially modulated light at asecond angle, wherein the second angle is greater than the first angle.

In embodiments, the light is pulsed. Accordingly, in embodiments, thesystem is configured so as any reflected signal is received by thedetector before the next light footprint irradiates the scene.Accordingly, the system can process any return signal before the nextlight footprint and no confusion between which footprint gave rise to areturn signal can occur. The skilled person will understand how tosynchronise the light source, holographic controller, spatial lightmodulator, light detector and any necessary processor in order toprovide this functionality and so a detailed description is not providedhere.

Each light footprint is formed using a corresponding computer-generatedhologram. Each computer-generated hologram is displayed on the spatiallight modulator in accordance with holographic data provided to thespatial light modulator. Each computer-generated hologram may becomprised of different data components. The data provides instructionsfor the spatial light modulator which individually address each lightmodulating pixel of the spatial light modulator. Specifically, the datamay provide instruction for each pixel on how much to modulate light. Inembodiments, the computer-generated hologram comprises first holographicdata defining the size and shape of the light footprint and secondholographic data defining the position of the light footprint in thescene. The first holographic data may include holographic data whichprovides an optical effect. In embodiments, the first holographic datacomprises a lensing function. As described above, the second holographicdata provides variable beam steering information. In embodiments, thesecond holographic data comprises a grating function.

FIG. 15 shows an embodiment comprising a processor 1570 in communicationwith the spatial light modulator 1510 and light detector 1520. Inoperation, processor 1570 is arranged to receive a light response signalfrom the light detector 1520 and a synchronisation information 1572 fromthe spatial light modulator 1510. Spatial light modulator 1510 isarranged to output spatially modulated light 1531 forming a lightfootprint (not shown) at a position in the scene. An object 1505 at theposition in the scene reflects spatially modulated light 1531 and thereflected light 1541 is detected by light detector 1520. Light detector1520 is configured to have a field of view including the scene.

For example, light detector 1520 may comprise a single light detectingelement (e.g. single photodiode) or an array of light detecting elements(e.g. one-dimensional or two-dimensional array of photodiodes),depending upon the light footprint and/or design requirements. Lightpulsing and synchronisation between the components of the system, aspreviously described, is used to determine a time of flight for thespatially modulated light as it travels from the spatial light modulator1510 to the light detector 1520 via the object 1505. This time of flightmeasurement can be used to determine the straight-line distance 1576from the spatial light modulator 1510 to the object 1505. Accordingly, alight detection and ranging (LIDAR) system is provided. In embodiments,at least one of a LIDAR emitter comprising the spatial light modulator1510 and a LIDAR receiver comprising the light detector 1520, may belocated within a lamp unit or a portable device or vehicle, such as theheadlamp unit of a vehicle. The processor 1570 may be located with theLIDAR emitter and/or the LIDAR detector or may be located remotely.

In embodiments, the light source is a laser. In embodiments, the lightdetector is a photodetector. In embodiments, there is provided a vehiclecomprising the LIDAR system.

In embodiments, the laser light from the light source may be modulatedwith a code that is unique to the LIDAR system. Such coding may be usedin order to avoid interference or confusion with light associated withother LIDAR systems (e.g. within other vehicles on the road). In suchembodiments, the LIDAR receiver looks for the coding in received light,and only processes received light modulated with the corresponding code.For example, binary modulation of the light amplitude with a uniquebinary number pattern may be performed to provide the unique code (e.g.by switching the light source on and off in a predetermined code orpattern). Other types of modulation or encoding of the laser light couldbe employed.

In some embodiments, two or more light sources may be used. For example,two or more lasers having different wavelengths (e.g. within the IRrange) may be included in the LIDAR system, and used at different timesto provide light to the SLM. The laser used as the light source, andthus the wavelength of light used for form the light footprint, may bechanged according to ambient conditions, such as when fog or otheradverse weather conditions are detected, to provide improved lightpenetration.

In embodiments, the LIDAR system may perform scanning at differentdistance ranges. For example, in embodiments, the holographic controllerof the LIDAR system may provide different temporal sequences ofholograms to the SLM for scanning the scene for respective distanceranges. In particular, the holographic data provided to the SLM may bedetermined so that the light footprint is focused at a replay planecorresponding to the required distance or range (e.g. by adjusting thelensing function corresponding to a Fourier Transform lens used toreconstruct the computer-generated hologram or by changing thecorresponding lensing data within the data, as described above). Inother embodiments, a physical Fourier Transform lens may be selected tofocus the light footprint at a replay plane corresponding the requireddistance or range. Thus, in embodiments, it may be said that the lightfootprint, or a parameter or element associated with the plurality ofcomputer-generated holograms that form the light footprint, isdetermined based on a distance range. In particular, the determinationis such that the light footprint is focused at a distance correspondingto the distance range.

The appropriate lensing function/data or physical Fourier Transform lensfor a particular range may be determined in response to a rangeselection signal. For example, a range selection signal may be providedmanually by a user, or automatically when a predetermined condition isdetected. The selection of the range may be based on vehicle speed,density of traffic or other driving factors or conditions. Selection ofa longer range scan may be preferred when the vehicle is travelling athigher speed. For example, a long range may be preferred for motorwaydriving and a short range may be preferred for city driving in densetraffic. Thus, in embodiments, the distance range is selected based on areceived signal. In embodiments the distance range is determined basedon at least one of: vehicle speed; ambient conditions; weatherconditions; traffic conditions and other driving parameters.

Although first, second and third groups of embodiments have been largelydisclosed separately, any feature of any embodiment or group ofembodiments may be combined with any other feature or combination offeatures of any embodiment or group of embodiments. That is, allpossible combinations and permutations of features disclosed in thepresent disclosure are envisaged.

In embodiments, the first light footprint may be formed of light of afirst wavelength and the second light footprint may formed of light of asecond wavelength. In embodiments, the first scan may be performed usinglight of a first wavelength and the second scan may be performed usinglight of a second wavelength. In embodiments, the first and secondwavelengths are different colours of visible light. In embodiments, oneor both of the first and second wavelengths are different wavelengths ofinfrared.

In embodiments, the system comprises a first spatial light modulator toform the first light footprint and a second spatial light modulator toform the second light footprint. In other embodiments, a single spatiallight modulator is used. For example, in embodiments, a first area of aspatial light modulator is allocated to the hologram forming the firstlight footprint and a second area of the spatial light modulator isallocated to the hologram forming the second light footprint.

The quality of the holographic reconstruction may be affect by theso-called zero order problem which is a consequence of the diffractivenature of using a pixelated spatial light modulator. Such zero-orderlight can be regarded as “noise” and includes for example specularlyreflected light (i.e. undiffracted light), and other unwanted light fromthe SLM.

In the example of Fourier holography, this “noise” is focused at thefocal point of the Fourier lens leading to a bright spot at the centreof the holographic reconstruction, known as the “DC spot”. The zeroorder light may be simply blocked out however this would mean replacingthe bright spot with a dark spot. Embodiments include an angularlyselective filter to remove only the collimated rays of the zero order.Embodiments also include the method of managing the zero-order describedin European patent 2,030,072 which is hereby incorporated in itsentirety by reference. In other embodiments, the spatial light modulatoris illuminated with diverging light such that the diffracted lightformed the light footprint is brought to a focus at the replay plane butthe zero-order light (which is not diffracted) continues diverging. Thezero order light is therefore effectively dispersed.

Whilst embodiments described herein include displaying one hologram perframe on the spatial light modulator, the present disclosure is by nomeans limited in this respect and more than one hologram may bedisplayed on the SLM at any one time. For example, embodiments implementthe technique of “tiling”, in which the surface area of the SLM isfurther divided up into a number of tiles, each of which is set in aphase distribution similar or identical to that of the original tile.Each tile is therefore of a smaller surface area than if the wholeallocated area of the SLM were used as one large phase pattern. Thesmaller the number of frequency component in the tile, the further apartthe reconstructed pixels are separated when the image is produced. Theimage is created within the zeroth diffraction order, and it ispreferred that the first and subsequent orders are displaced far enoughso as not to overlap with the image and may be blocked by way of aspatial filter.

As mentioned above, the holographic reconstruction produced by thismethod (whether with tiling or without) comprises spots that form imagepixels. The higher the number of tiles used, the smaller these spotsbecome. If one takes the example of a Fourier transform of an infinitesine wave, a single frequency is produced. This is the optimum output.In practice, if just one tile is used, this corresponds to an input of asingle cycle of a sine wave, with zero values extending in the positiveand negative directions from the end nodes of the sine wave to infinity.Instead of a single frequency being produced from its Fourier transform,the principle frequency component is produced with a series of adjacentfrequency components on either side of it. The use of tiling reduces themagnitude of these adjacent frequency components and as a direct resultof this, less interference (constructive or destructive) occurs betweenadjacent image pixels, thereby improving the image quality. Preferably,each tile is a whole tile, although embodiments use fractions of a tile.

The methods and processes described herein may be embodied on acomputer-readable medium. The term “computer-readable medium” includes amedium arranged to store data temporarily or permanently such asrandom-access memory (RAM), read-only memory (ROM), buffer memory, flashmemory, and cache memory. The term “computer-readable medium” shall alsobe taken to include any medium, or combination of multiple media, thatis capable of storing instructions for execution by a machine such thatthe instructions, when executed by one or more processors, cause themachine to perform any one or more of the methodologies describedherein, in whole or in part.

The term “computer-readable medium” also encompasses cloud-based storagesystems. The term “computer-readable medium” includes, but is notlimited to, one or more tangible and non-transitory data repositories(e.g., data volumes) in the example form of a solid-state memory chip,an optical disc, a magnetic disc, or any suitable combination thereof.In some example embodiments, the instructions for execution may becommunicated by a carrier medium. Examples of such a carrier mediuminclude a transient medium (e.g., a propagating signal that communicatesinstructions).

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thescope of the appended claims. The present disclosure covers allmodifications and variations within the scope of the appended claims andtheir equivalents.

The following items are disclosed:

Item 1. A light detection and ranging, “LIDAR”, system arranged to scana scene, the system comprising:

-   -   a light source arranged to output light having a first        characteristic;    -   a spatial light modulator, “SLM”, arranged to receive the light        from the light source and output spatially-modulated light in        accordance with computer-generated holograms represented on the        spatial light modulator;    -   a holographic controller arranged to output a plurality of        computer-generated holograms to the spatial light modulator,        wherein each computer-generated hologram is arranged to form a        corresponding light footprint within the scene and the        holographic controller is further arranged to change the        position of the light footprint within the scene; and    -   a light detector arranged to receive light having the first        characteristic from the scene and output a light response        signal.

Item 2. A LIDAR system as defined in item 1, wherein the plurality ofcomputer-generated holograms comprise a first plurality ofcomputer-generated holograms arranged to provide a first scan within thescene, and wherein the holographic controller is arranged to receive thelight response signal in response to the first scan and determine asecond plurality of computer-generated holograms based on a property ofthe light response signal in response to the first scan.

Item 3. A LIDAR system as defined in item 2 wherein the second pluralityof computer-generated holograms are arranged to provide a second scanwithin the scene.

Item 4. A LIDAR system as defined in item 3 wherein the first scan is ascan of a first area of the scene and the second scan is a scan of asecond area of the scene.

Item 5. A LIDAR system as defined in item 3 or 4 wherein the first scanis a scan in a first direction of the first area of the scene and thesecond scan is a scan in a second direction of the first area of thescene.

Item 6. A LIDAR system as defined in any of items 2 to 5 wherein thefirst plurality of computer-generated holograms are arranged to form afirst light footprint having a first area and the second plurality ofcomputer-generated holograms are arranged to form a second lightfootprint having a second area, wherein the first area is not equal tothe second area.

Item 7. A LIDAR system as defined in item 6 wherein the first lightfootprint has a substantially one-dimensional shape extending in asecond direction and the second light footprint has a substantiallyone-dimensional shape extending in a first direction.

Item 8. A LIDAR system as defined in item 1 wherein the plurality ofcomputer-generated holograms comprise a first computer-generatedhologram arranged to form a first light footprint at a first position inthe scene and a second computer-generated hologram arranged to form asecond light footprint at a second position in the scene, wherein outputof the second computer-generated hologram immediately follows output ofthe first computer-generated hologram.

Item 9. A LIDAR system as defined in item 8 wherein the first positionis spatially separated from the second position.

Item 10. A LIDAR system as defined in item 9 wherein the first positionis substantially adjacent the second position.

Item 11. A LIDAR system as defined in any of items 8 to 10 wherein thelight footprint is continuously repositioned so as to scan the lightfootprint within the scene.

Item 12. A LIDAR system as defined in any of items 8 to 11 wherein thefirst light footprint has a first area and the second light footprinthas a second area, wherein the first area is not equal to the secondarea.

Item 13. A LIDAR system as defined in any of items 8 to 12 wherein thefirst light footprint has a first shape and the second light footprinthas a second shape, wherein the first shape is different to the secondshape.

Item 14. A LIDAR system as defined in any of items 8 to 13 wherein thefirst light footprint has a shape having a first orientation and thesecond light footprint has a shape having a second orientation, whereinthe first orientation is different to the second orientation.

Item 15. A LIDAR system as defined in item 14 wherein the shape is asubstantially one-dimensional shape.

Item 16. A LIDAR system as defined in items 14 or 15 wherein the firstorientation is perpendicular to the second orientation.

Item 17. A LIDAR system as defined in item 1 wherein the plurality ofcomputer-generated holograms comprise a first plurality ofcomputer-generated holograms arranged to provide a first scan within thescene and a second plurality of computer-generated holograms arranged toprovide a second scan within the scene.

Item 18. A LIDAR system as defined in item 17 wherein the firstplurality of computer-generated holograms and second plurality ofcomputer-generated holograms are interleaved.

Item 19. A LIDAR system as defined in item 17 or 18 wherein the firstscan is a scan of a first area of the scene and the second scan is ascan of a second area of the scene.

Item 20. A LIDAR system as defined in item 19 wherein the second area isspatially separated from the first area.

Item 21. A LIDAR system as defined in item 19 or 20 wherein theplurality of computer-generated holograms are arranged to scan the firstarea and second area by moving spatially-modulated light back and forthbetween the first area and second area.

Item 22. A LIDAR system as defined in any of items 17 to 21 wherein thefirst plurality of computer-generated holograms arranged to perform thefirst scan are arranged to form a light footprint at a plurality ofrandom positions within the scene.

Item 23. A LIDAR system as defined in item 22 wherein the first scan iscontinuous.

Item 24. A LIDAR system as defined in item 22 or 23 wherein the secondplurality of computer-generated holograms are arranged to perform thesecond scan of an area within the scene.

Item 25. A LIDAR system as defined in item 24 wherein the area isdetermined based on a property of the light response signal in responseto the first scan.

Item 26. A LIDAR system as defined in any of items 17 to 25 wherein thefirst scan is a scan in a first direction and the second scan is a scanin a second direction.

Item 27. A LIDAR system as defined in any of items 17 to 26 wherein thefirst plurality of computer-generated holograms are arranged to form afirst light footprint having a first area and the second plurality ofcomputer-generated holograms are arranged to form a second lightfootprint having a second area, wherein the first area is not equal tothe second area.

Item 28. A LIDAR system as defined in item 27 wherein the first lightfootprint has a substantially one-dimensional shape extending in asecond direction and the second light footprint has a substantiallyone-dimensional shape extending in a first direction.

Item 29. A LIDAR system as defined in any preceding item wherein eachcomputer-generated hologram is a phase-only hologram.

Item 30. A LIDAR system as defined in any preceding item wherein thespatially modulated light output by the SLM is encoded with a code thatis unique to the LIDAR system.

Item 31. A LIDAR system as defined in item 30 wherein the spatiallymodulated light output by the SLM is encoded by modulation of the lightamplitude.

Item 32. A LIDAR system as defined in any preceding item comprisingfirst and second light sources configured to output light of differentwavelengths to the SLM.

Item 33. A LIDAR system as defined in item 32 wherein one of the firstand second light sources is selected based on ambient conditions.

Item 34. A LIDAR system as defined in any preceding item wherein thelight footprint, or a parameter or element associated with the pluralityof computer-generated holograms that form the light footprint, isdetermined based on a received signal.

Item 35. A LIDAR system as defined in item 34 wherein the receivedsignal provides an indication of at least one of: vehicle speed; ambientconditions; weather conditions; traffic conditions and other drivingparameters.

Item 36. A LIDAR system as defined in any preceding item wherein thelight footprint, or the parameter or element associated with theplurality of computer-generated holograms that form the light footprint,is determined based on a distance range.

Item 37. A LIDAR system as defined in item 36 wherein the lightfootprint, or the parameter associated with the plurality ofcomputer-generated holograms that form the light footprint, isdetermined so as to focus the light footprint at a distancecorresponding to a distance range.

Item 38. A LIDAR system as defined in item 36 or 37 wherein the distancerange is selected based on at least one of: vehicle speed; ambientconditions; weather conditions; traffic conditions and other drivingparameters.

Item 39. A LIDAR system as defined in any preceding item furthercomprising an angular magnification system arranged to magnify theangular deflection of the spatially-modulated light from the spatiallight modulator.

Item 40. A LIDAR system as defined in item 39 wherein the angularmagnification system is arranged to refract the spatially-modulatedlight.

Item 41. A LIDAR system as defined in item 39 or 40 wherein the angularmagnification system is arranged to receive the spatially modulatedlight at a first angle and output the spatially modulated light at asecond angle, wherein the second angle is greater than the first angle.

Item 42. A LIDAR system as defined in any preceding item wherein thefirst characteristic is amplitude modulation at a first frequency.

Item 43. A LIDAR system as defined in any preceding item wherein thelight is pulsed.

Item 44. A LIDAR system as defined in any preceding item wherein thespatial light modulator is a liquid crystal on silicon, “LCOS”, spatiallight modulator.

Item 45. A LIDAR system as defined in any preceding item wherein eachcomputer-generated hologram comprises first holographic data definingthe size and shape of the light footprint and second holographic datadefining the position of the light footprint in the scene.

Item 46. A LIDAR system as defined in any preceding item wherein thefirst holographic data comprises a lensing function.

Item 47. A LIDAR system as defined in any preceding item wherein thesecond holographic data comprises a grating function.

Item 48. A LIDAR system as defined in any preceding item furthercomprising a processor arranged to determine a distance of an object inthe scene from the LIDAR system by measuring a time difference betweenoutput of first spatially-modulated light, corresponding to a firstcomputer-generated hologram of the plurality of computer-generatedholograms, and detection of first spatially-modulated light reflectedfrom the object.

Item 49. A LIDAR system as defined in any preceding item wherein thelight detector comprises one of: a single light detecting element or anarray of light detecting elements.

Item 50. A LIDAR system as defined in any preceding item wherein atleast one of the SLM and the light detector is located within a lampunit of a portable device or vehicle.

Item 51. A lamp unit comprising the LIDAR system of any preceding item.

Item 52. A vehicle comprising the LIDAR system of any preceding item.

The invention claimed is:
 1. A light detection and ranging, “LIDAR”,system arranged to scan a scene, the system comprising: a light sourcearranged to output light having a first characteristic; a spatial lightmodulator, “SLM”, arranged to receive the light from the light sourceand output spatially-modulated light in accordance withcomputer-generated holograms represented on the spatial light modulator;a holographic controller arranged to output a plurality ofcomputer-generated holograms to the spatial light modulator, whereineach computer-generated hologram is arranged to form a correspondinglight footprint within the scene and the holographic controller isfurther arranged to change the position of the light footprint withinthe scene; and a light detector arranged to receive light having thefirst characteristic from the scene and output a light response signal,wherein the plurality of computer-generated holograms comprise a firstcomputer-generated hologram arranged to form a first light footprint ata first position in the scene and a second computer-generated hologramarranged to form a second light footprint at a second position in thescene, wherein output of the second computer-generated hologramimmediately follows output of the first computer-generated hologram, andwherein the first light footprint has a first area and the second lightfootprint has a second area, wherein the first area is not equal to thesecond area.
 2. A LIDAR system as claimed in claim 1, wherein theplurality of computer-generated holograms comprise a first plurality ofcomputer-generated holograms arranged to provide a first scan within thescene, and wherein the holographic controller is arranged to receive thelight response signal in response to the first scan and determine asecond plurality of computer-generated holograms based on a property ofthe light response signal in response to the first scan.
 3. A LIDARsystem as claimed in claim 2 wherein the second plurality ofcomputer-generated holograms are arranged to provide a second scanwithin the scene, wherein the first scan is a scan of a first area ofthe scene and the second scan is a scan of a second area of the scene.4. A LIDAR system as claimed in claim 1 wherein the first lightfootprint has a one-dimensional shape extending in a second directionand the second light footprint has a one-dimensional shape extending ina first direction.
 5. A LIDAR system as claimed in claim 1 wherein thelight footprint is continuously repositioned so as to scan the lightfootprint within the scene.
 6. A LIDAR system as claimed in claim 1wherein one or more of the following conditions (1)-(3) is met: (1) thefirst light footprint has a first shape and the second light footprinthas a second shape, wherein the first shape is different to the secondshape; (2) the first light footprint has a shape having a firstorientation and the second light footprint has a shape having a secondorientation, wherein the first orientation is different to the secondorientation; and (3) the first position is spatially separated from thesecond position.
 7. A LIDAR system as claimed in claim 1 wherein eachcomputer-generated hologram is a phase-only hologram.
 8. A LIDAR systemas claimed in claim 1 wherein the spatially modulated light output bythe SLM is encoded with a code that is unique to the LIDAR system.
 9. ALIDAR system as claimed in claim 8 wherein the spatially modulated lightoutput by the SLM is encoded by modulation of the light amplitude.
 10. ALIDAR system as claimed in claim 1 comprising first and second lightsources configured to output light of different wavelengths to the SLM.11. A LIDAR system as claimed in claim 1 wherein the light footprint, ora parameter or element associated with the plurality ofcomputer-generated holograms that form the light footprint, isdetermined based on a received signal.
 12. A LIDAR system as claimed inclaim 11 wherein the received signal provides an indication of at leastone of: vehicle speed; ambient conditions; weather conditions; trafficconditions and other driving parameters.
 13. A LIDAR system as claimedin claim 1 wherein the light footprint, or a parameter associated withthe plurality of computer-generated holograms that form the lightfootprint, is determined so as to focus the light footprint at adistance corresponding to a distance range.
 14. A LIDAR system asclaimed in claim 1 further comprising an angular magnification systemarranged to magnify the angular deflection of the spatially-modulatedlight from the spatial light modulator, wherein the angularmagnification system is arranged to receive the spatially modulatedlight at a first angle and output the spatially modulated light at asecond angle, wherein the second angle is greater than the first angle.15. A LIDAR system as claimed in claim 1 wherein the firstcharacteristic is amplitude modulation at a first frequency.
 16. A LIDARsystem as claimed in claim 1 wherein each computer-generated hologramcomprises first holographic data defining the size and shape of thelight footprint and second holographic data defining the position of thelight footprint in the scene.
 17. A LIDAR system as claimed in claim 1wherein the first holographic data comprises a lensing function, andwherein the second holographic data comprises a grating function.
 18. ALIDAR system as claimed in claim 1 further comprising a processorarranged to determine a distance of an object in the scene from theLIDAR system by measuring a time difference between output of firstspatially-modulated light, corresponding to a first computer-generatedhologram of the plurality of computer-generated holograms, and detectionof first spatially-modulated light reflected from the object.
 19. ALIDAR system as claimed in claim 1 wherein at least one of the SLM andthe light detector is located within a lamp unit of a portable device orvehicle.
 20. A lamp unit comprising the LIDAR system of claim
 1. 21. Avehicle comprising the LIDAR system of claim
 1. 22. A method forscanning a scene using LIDAR, the method comprising: providing lighthaving a first characteristic; receiving the light having the firstcharacteristic on a spatial light modulator; providing a plurality ofcomputer-generated holograms to the spatial light modulator andrepresenting the plurality of computer-generated holograms on thespatial light modulator, outputting spatially-modulated light having thefirst characteristic from the spatial light modulator in accordance withthe plurality of computer-generated holograms to provide a lightfootprint within the scene, the plurality of spatially-modulatedholograms changing a position of the light footprint within the scene;and receiving light having the first characteristic from the scene at alight detector and outputting a light response signal from the lightdetector, wherein the plurality of computer-generated holograms comprisea first computer-generated hologram arranged to form a first lightfootprint at a first position in the scene and a secondcomputer-generated hologram arranged to form a second light footprint ata second position in the scene, wherein output of the secondcomputer-generated hologram immediately follows output of the firstcomputer-generated hologram, and wherein the first light footprint has afirst area and the second light footprint has a second area, wherein thefirst area is not equal to the second area.